SCB initiator

ABSTRACT

A detonator for high explosives initiated by mechanical impact includes a cylindrical barrel, a layer of flyer material mechanically covering the barrel at one end, and a semiconductor bridge ignitor including a pair of electrically conductive pads connected by a semiconductor bridge. The bridge is in operational contact with the layer, whereby ignition of said bridge forces a portion of the layer through the barrel to detonate the explosive. Input means are provided for igniting the semiconductor bridge ignitor.

The U.S. Government has rights in this invention pursuant to ContractNo. DE-AC04-76DP00789 between the Department of Energy and AT&TTechnologies, Inc.

BACKGROUND OF THE INVENTION

This invention relates generally to an improved detonator, and moreparticularly, to a semiconductor bridge (SCB) actuated detonator forhigh explosives.

The inexpensive and reliable ignition of explosives is a desirable goalfor obvious cost and safety reasons. To this end, the semiconductorbridge (SCB) igniter of R. Bickes et al., U.S. Pat. No. 4,708,060, wasdeveloped. This invention has a short semiconductor bridge between twospaced metal pads on a nonconducting substrate. The heavily doped,approximately one ohm, bridge is in contact with an explosive material.The bridge is easily designed to not fire when a "no fire" current isapplied, but to fire when a higher "fire" current is applied. Asdisclosed, application of a 15A, 15 us current pulse through the SCBproduces a plasma discharge that ignites the explosive material at arelatively slow rate. Such ignition is suitable for actuators, gasgenerators and rocket motors, but is not fast enough for otherapplications.

In some applications, high explosive powders are initiated by themechanical impulse provided by a slapper detonator, a piece of hardmaterial rapidly propelled against the powder by an electricallyexploded metal foil. Because a slapper can generate detonation promptly,this technology can be used wherever exploding bridge wire devices arenormally used to initiate these high explosives. The use of a slapperinitiator permits the use of more stable explosives, an important safetyconsideration.

In addition, exploding bridge wires have also been used for directinitiation of high explosives, a construction that eliminates theslapper structure.

SUMMARY OF THE INVENTION

It is an object of this invention to use an SCB as the exploding foil ina slapper detonator.

It is another object of this invention to use a high current pulse tocause an SCB to function as a slapper detonator.

It is still another object of this invention to provide a low inductancecapacitor to discharge into an SCB to initiate it as a slapperdetonator.

It is also an object of this invention to use an SCB for direct and veryprompt initiation of a high explosive.

It is a further object of this invention to provide a laser to arm anundoped SCB either for direct initiation or in a slapper detonator.

Additional objects, advantages, and novel features of the invention willbecome apparent to those skilled in the art upon examination of thefollowing description or may be learned by practice of the invention.The objects and advantages of the invention may be realized and attainedby means of the instrumentalities and combinations particularly pointedout in the appended claims.

To achieve the foregoing and other objects, and in accordance with thepurpose of the present invention, as embodied and broadly describedherein, a first embodiment of the present invention may comprise adetonator for high explosives initiated by mechanical impact, thedetonator comprising a cylindrical barrel or spacer having a tubularopening extending from an output end, mechanically coupled to anexplosive, to an input end, a layer of flyer material mechanicallycovering the tubular opening at the input end, and a semiconductorbridge ignitor including an pair of electrically conductive padsconnected by a semiconductor bridge, the bridge being in operationalcontact with the layer. Ignition of the bridge forces a portion of thelayer through the barrel at high velocity to detonate the explosive uponimpact. Input means are provided for igniting the semiconductor bridgeignitor. A second embodiment of the present invention is similar to thefirst embodiment except that the high explosive is in direct contactwith the SCB, with no cylindrical barrel or flyer material being used.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form part ofthe specification, illustrate an embodiment of the present inventionand, together with the description, serve to explain the principles ofthe invention.

FIG. 1 shows a first embodiment of the invention.

FIG. 2 shows a second version of the first embodiment of the invention.

FIG. 3 shows a second embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a first embodiment of the invention where a flyer assembly10 for initiating a high explosive is actuated by an input circuit 30.

Flyer assembly 10 may comprise a substrate 11 (shown in FIG. 2) uponwhich a SCB 12 is formed as taught by U.S. Pat. No. 4,708,060, thedisclosure of this patent being incorporated herein by reference. SCB 12typically includes a highly doped silicon layer 18 on a substrate 11 andhaving metallized lands 14 and 16 at opposite ends, forming a bridgetherebetween. Lands 14 and 16 may be connected to input circuit 30 bysolder connections (not shown), or by other methods such asthermocompressive or ultrasonic bonds.

A nonconductive plastic flyer layer 20, typically 1 to 3 mil thick, isplaced over the SCB. A hard nonconductive barrel or spacer 22, typicallysapphire, having an inside diameter of about 20 mils and a thickness ofabout 20 mils, is placed over flyer layer 20 and bridge 18. A highexplosive 28 such as PETN or HNS is adjacent the output end 26 of barrel22.

In operation, when a low inductance input circuit 30 provides a fastrise-time pulse on the order of 1000 amps to flyer assembly 10, bridge18 vaporizes and explodes with sufficient energy to force flyer layer 20against the input end 24 of barrel 22. The portion of layer 20 abuttingbarrel 22 is prevented from movement away from substrate 11 by theinertia of barrel 22. However, a portion of flyer layer 20 is sheared bythe inside edge and passes through the central portion of barrel 20.This "flying" portion hits explosive 28 with sufficient energy todetonate the explosive. This operation differs from the teaching of U.S.Pat. No. 4,708,060 in that an SCB could safely be ignited with arelatively low power source.

FIG. 2 shows a preferred embodiment of the invention of FIG. 1. A topview of the input circuit is shown to the left of the dashed line inFIG. 2 marked "90°", while a cut-away side view is shown for the flyerassembly 10 of FIG. 1 to the right of the dashed line. A low inductance0.02 uF capacitor 34 is preferably formed from approximately a 2 footarc of a 1 foot radius circle of stripline material including top andbottom thin metallic films 33 and 31 separated by an insulating Kaptonlayer 35 having a thickness on the order of 1-3 mils. A dc voltage, V+,perferably on the order of 1-3 kV, is applied to one surface ofcapacitor 34; the return voltage, V-, is applied to the oppositesurface. The stripline forming the one surface of capacitor 34 extendsas short a distance as possible, to minimize inductance, to the inputterminal of a low inductance, high voltage, fast, electronic switch 36.A suitable switch is disclosed in U.S. Pat. No. 3,663,855. The triggercircuit of switch 36 is connected to a trigger circuit as is well knownin the art. The output of switch 36 is connected by a short striplinesection 33 to the metallic land 16 of the SCB as described above. SCBbridge layer 18 generally abuts Kapton layer 35, although thethicknesses of the two layers may not be identical. SCB substrate 11covers the side of layer 18 opposite lands 16 and 14.

For an SCB as disclosed in U.S. Pat. No. 4,708,060, layer 18 may beeither doped silicon or polysilicon, and substrate 11 is either sapphireor silicon. However, an alternative version of the invention is alsoshown in FIG. 2 to include laser 40 which focuses laser beam 42 througha sapphire substrate 11 to an undoped silicon bridge 18'. For thisversion, layer 18' is undoped silicon with a high impedance thatnormally acts as an open switch in the circuit. Substrate 11 is sapphireor other material transparent to laser beam 42. Irradiation of undopedsilicon 18' by laser 42 of sufficient energy and appropriate wavelengthcreates electrical carriers in the silicon via the photoconductiveeffect, thereby reducing the impedance of silicon 18' to approximatelyone ohm. Application of the input signal during this laser applicationcauses ignition in a manner similar to the doped SCB.

FIG. 3 shows a second embodiment of the invention where the energy ofthe SCB directly ignites a high explosive 28 upon the application of acurrent pulse similar to that described in the first embodiment. In thisfigure, everything to the left of the vertical line marked 90° isunderstood to be similar to the structure of FIGS. 1 and 2. The SCBbridge may be doped silicon 18 on an insulating substrate 35; it mayalso be undoped silicon 18' on sapphire 11 with irradiation by laser 40discussed above. Metal land 16 is connected to the input circuit, metalland 14 is connected to ground. High explosive 28 is in direct contactwith the bridge 18 or 18'. When sufficient energy is applied from inputcircuit 30, the SCB ignites with sufficient energy to initiate theexplosion.

The particular sizes and equipment discussed above are cited merely toillustrate a particular embodiment of this invention. It is contemplatedthat the use of the invention may involve components having differentsizes and shapes as long as the principle, using a low inductance inputcircuit to fire a SCB to detonate high explosives, is followed. It isintended that the scope of the invention be defined by the claimsappended hereto.

We claim:
 1. A detonator for high explosives initiated by mechanicalimpact, said detonator comprising:a layer of flyer material; asubstrate; a semiconductor bridge ignitor on said substrate including apair of electrically conductive pads connected by a semiconductorbridge, said bridge being in operational contact with said layer,whereby ignition of said bridge forces a portion of said layer throughsaid barrel to detonate the explosive; and input means for igniting saidsemiconductor bridge ignitor.
 2. The detonator of claim 1 wherein saidinput means comprises:capacitor means for storing electrical energy;switch means for switching electrical energy, said switch means havingan input port connected to said capacitor, an output port connected tosaid semiconductor bridge ignitor, and a trigger port for receiving atrigger signal for closing said switch to fire said ignitor.
 3. Thedetonator of claim 1 wherein said semiconductor bridge is highly doped.4. The detonator of claim 1 further comprising a cylindrical barrelhaving a tubular opening extending from an output end, mechanicallycoupled to the explosive, to an input end adjacent said flyer material.5. The detonator of claim 1 wherein said semiconductor bridge is undopedsilicon and said substrate is sapphire, and further comprising:lasermeans for directing a laser beam onto said bridge through said substrateto reduce the impedance of said bridge prior to ignition of said inputmeans.
 6. A detonator for high explosives comprising:a semiconductorbridge ignitor including an pair of electrically conductive padsconnected by a semiconductor bridge, said bridge being in direct contactwith said explosive; and input means for providing sufficient electricalenergy to said bridge to ignite said ignitor and detonate the explosive.7. The detonator of claim 6 wherein said semiconductor bridge is notdoped, said detonator further comprising laser means for directing alaser beam onto said bridge to lower the impedance of said bridge.